1. Field of the Invention
The present invention relates to an image normalization processing system for carrying out normalization processing on an image having been read, and more specifically, to an image normalization processing system wherein a normalization processing condition determined by an image reading apparatus can be changed by an image receiving apparatus.
2. Description of the Related Art
Radiation image information reading apparatuses (CR apparatuses; Computed Radiography) which read radiation image information by detecting light emitted in accordance with the radiation image information stored on a stimulable phosphon sheet (hereinafter simply called a “sheet”) upon exposure to stimulating rays, such as a laser beam irradiated on the sheet, have been known (see Japanese Unexamined Patent Publication No. 62(1987)-18536, for example). Images (image data) read by such a CR apparatus are used in a medical facility for diagnosing a lesion, injury and the like and the degree thereof by being output as visible images displayed on a CRT display or printed on a film by an LP (laser printer), for example.
In the CR apparatus, light beam scan means scans an entire sheet by using a laser beam for example, and leads the light emitted from the sheet via a light guide, to reading means comprising a photoelectric converter such as a photomultiplier tube to convert the emitted light into an electric signal (image signal). Signal processing means carries out predetermined image signal processing on the obtained image signal. By using the processed image signal, the radiation image information is output as a visible image on a recording material such as a photosensitive material or on a display apparatus such as a CRT. In this manner, a radiation image which is not affected by a change in radiation exposure can be obtained.
The signal processing means converts the image signal read by the reading means into a logarithm by using a logarithmic amplifier, for example. The image signal converted into a logarithm is then converted into digital image data by using an analog/digital converter. After desired image processing such as frequency processing or tone processing has been carried out on the image data, the signal processing means converts the image data into a TV image signal according to the NTCS system or the like, and outputs the image signal as a visible image.
Following the recent advancement in technologies for communications and computers, a system (medical network system) wherein a CR apparatus and an image receiving apparatus such as a diagnostic workstation are connected to a network has been installed in a hospital so that a computer can be used for diagnosis or the like at a location remote from the CR apparatus.
In the CR apparatus, a normalization processing condition is determined in order to cause the density or the contrast of the output visible image to be in an appropriate range. Normalization processing is carried out under the normalization processing condition on the image data read by the reading means and predetermined image processing such as frequency processing is also carried out on the image data if necessary. Based on the image data after the image processing, the visible image is output. On this occasion, after the normalization processing, image data before the normalization processing are not saved.
In a medical network system such as the one described above, image data which are obtained by image processing using a predetermined image processing condition on the normalization processing image data, or the image processing condition and the image data before the image processing, that is, the image processing condition and the post-normalization processing image data, are transferred from the CR apparatus to the image receiving apparatus.
The “normalization processing” herein referred to means signal processing for adjusting the image data read by the reading means to an input signal range of image processing means so that the visible image to be output can have an appropriate density range. For example, a condition such as a gain and a data range of the reading means (the condition set here is called a “normalization processing condition”) is determined so that maximal and minimal amounts of the emitted light from a range of image information useful for diagnosis out of radiation image information read by the reading means can respectively correspond to maximal and minimal values of the appropriate density range of the output visible image and a density resolution optimal for diagnosis can also be obtained for the range of the diagnostically useful image information. Under the determined normalization processing condition, the image data read by the reading means are converted into image data to be input to the image processing means. In order to determine the “normalization processing condition”, various kinds of parameters are used. More specifically, parameters which are determined based on photographing menus, such as photographing of chest and head, and are used for recognizing a pattern of the images, parameters for finding a characteristic value through generation of a histogram of image data, and the like can be listed as those parameters. As the parameters for recognizing the image pattern, partitioned photographing recognition parameters for recognizing the cases of partitioned photographing, parameters for selecting an algorithm for recognizing the case of radiation field restriction, and various kinds of radiation field recognition parameters such as radiation field detection threshold values can be listed. As for the parameters regarding a histogram, parameters for selecting an algorithm for histogram analysis or various kinds of histogram analysis parameters such as histogram analysis threshold values can be used.
The above normalization processing uses only the information corresponding to the input signal range out of the radiation image information read by the reading means, and discards all out-of-range radiation image information. Therefore, image data after normalization processing, that is, the image data to be input to the image processing means, do not include data corresponding to radiation image information which is out of the desired input signal range.
For this reason, when the normalization processing has a problem such as inappropriate setting of the desired image information range, the radiation image information once discarded cannot be restored even when the radiation image information obtained by photographing a subject and reading the image by using the reading means is appropriate. Therefore, no retrial of appropriate normalization processing using the same photographed image has been possible. In order to carry out appropriate normalization processing, the only method is to photograph again by changing the normalization processing condition. It is thus difficult to obtain radiation image information which is the same as the one read before, and this is inconvenient for diagnostic purposes.
Especially, in a medical network system, diagnosis is not carried out in parallel with reading of the image by the CR apparatus. It is generally carried out later by reading an image transferred from the CR apparatus and stored in a recording apparatus. Therefore, when there is a problem in the normalization processing carried out by the CR apparatus, the image receiving apparatus cannot solve the problem and re-photographing is rarely possible.